Polyolefins have conventionally been used in a wide application as various molded articles, sheets, etc. because of their excellent molding properties, toughness, water resistance, organic solvent resistance, and chemical resistance, low specific viscosity, and inexpensiveness. However, the polyolefins are insufficient in heat resistance, leaving room for improvement, which has given rise to a bar to broadening of application.
On the other hand, polyphenylene ether resins are excellent in heat resistance but unsatisfactory in molding properties and solvent resistance, thus finding limited applications to be made of them. In order to improve molding properties, impact strength, and the like, polyblends of polyphenylene ether resins with, for example, styrene resins have been employed. However, the range of their application is still limited to poor solvent resistance. For example, these polyblends are unsuitable in the field requiring resistance to oils, such as gasoline.
A number of blend compositions of polyolefins and polyphenylene ethers have been proposed aiming at compensation for the respective disadvantages while retaining the respective advantages inherently possessed. For instance, the composition disclosed in Japanese Patent Publication No. 7069/67 has been developed for the purpose of improving molding properties and tensile properties. However, it does not always attain the relatively high level of mechanical strength demanded in industry. Further, for the purpose of improving compatibility between polyolefins and polyphenylene ether resins to thereby enhance mechanical strength, there have been proposed compositions having incorporated therein a styrene/butadiene block copolymer or a hydrogenated product thereof as disclosed in Japanese Laid-Open patent application Nos. 71158/78, 88960/79, and 100159/84 and compositions comprising these components and, in addition, inorganic fillers as disclosed in Japanese Laid-Open patent application No. 103556/83. Although these compositions show improvements in molding properties and mechanical strength, they fail to take full advantage of organic solvent resistance inherent to polyolefins from the reason that the compounding ratio of the polyolefin is small or the matrix (continuous phase) consists of the polyphenylene ether resin or a combination of the polyphenylene ether resin and a styrene resin. It has also been proposed to blend a polyphenylene ether resin with a large amount exceeding 20% by weight of polyolefin and further add, as a compatibilizer, a diblock copolymer or a radial teleblock copolymer comprising an alkenyl aromatic compound and a conjugated diene or a hydrogenated product thereof as disclosed in Japanese Laid-Open patent application Nos. 103557/83 and 76547/85. These publications state that compatibility between a polyphenylene ether resin and low-density polyethylene as polyolefin can be improved by compounding a hydrogenated diblock copolymer of an alkenyl aromatic compound and a conjugated diene thereby bringing about improvements on tensile properties, brittleness, and the like. However, only the improvement in compatibility is not enough to satisfy various performance requirements generally demanded for resins. More specifically, the composition of three-component system disclosed in Japanese Laid-Open application No. 76547/85 which comprises polyphenylene ether, a large proportion of low-density polyethylene as polyolefin, and, as a compatibilizer, a hydrogenated diblock copolymer of an alkenyl aromatic compound and a conjugated diene has limitations on its use due to seriously inferior stiffness. The resin composition of the same system using polypropylene as a polyolefin achieves some improvement on stiffness and heat resistance, but there is still room for further improvements for practical use.